X-ray apparatus



Aug. 18, 1925. 1,550,507

W. D. COOLUDGE X-RAY APPARATUS Filed July 9, 1920 Fig. l F: 2.

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5 d wr M His'Attornes.

Patented Aug. 18, 1925.

uurrao STATES PATENT OFFICE.

WILLIAI D. COOLIDGE, OF SCHENECTADY, NEW YORK, ASSIGNOR '10 GENERAL ELEC- I 'IBIG COMPANY, A CORPORATION OF NEW YORK.

x-RAY APPARATUS.

Application filed July 9, 1920. Serial- No. 895,088.

To all whoin it may comer n: I

Be it known that I, WILLIAM D. CooLIocn, a citizen of the United States, residing at Schenectady, in the county .of Schenectady, State of New York, have invented certam new and useful Improvements in X-Ray Apparatus, of which the following is a specification.

The present invention comprises an X- ray ap aratus which is particularly suited for ra iography altho it is not limited in its use to this particular pur use.

When utilizing X-rays or diagnostic purposes, it is particularly desirable to secure a constant radio raphic effect for a given setting so that or comparison purposes the resulting radiographs may be of equal density. For'exampllce, for a constant impressed voltage and -ray producing current, and for a given subject, an X-ray tube 0 rating by electron conduction sub stantia ly independently of gaseous ionization, will always. roduce a radiograph of the same densit or a given exposure. As explained b American ournal of Roentgenology, vol. 3 (1916), page 300, the radiographic effect may be expressed as follows in terms of cur rent (I), time (T), voltage (V), and distance. (D) 1 The distance between the -X-ray source and the photographic plate or film can read ily be maintained constant. It would appear in view of this that with a given patient, a doctor or dentist could always get the same sort of radiograph by the use of a simple time switch. As a matterof fact, this ideal condition is obtainable only in a laboratory under carefully controlled conditions. Ordinarily the available current supply is extremely variable in voltage, and consequently a time switch alone is insuifi cient to give a substantially constant radlographic effect.

In accordance with my invention, I have provided an X-ray apparatus constructed to give a substantially constant radiographic effect even with a variable supply voltage. The novel structural features of my invention will be pointed out with particularity in the appended claims.

rof. J. S. Shearer in the" My invention will be described in detail in the following specification taken in connection with the accompanying drawings in which Fig. 1 illustrates diagrammaticall a system embod ing my invention utilizing an ordinary time switch; Fig. 2 is a diagram of a set of curves showing the currents in the transformer furnishing current for heating the cathode of the X-ray tube; Fig. 3 is a more highly developed system containing a special time switch with a constant or substantiall emission at the catho e; and Fig. 4 illustrates diagrammatically one form of cathode heating transformer suitable for use in my im proved apparatus.

he system shown in Fig. 1 contains an X-ray tube 1 of the hot cathode type supplied with heating currents from a s ecial transforming apparatus 3 which is designed to g1ve a heating effect which varies inversely with the supply voltage. In the con-. structlon illustrated in Fig. 1 and Fig. 4, the transformer 3 is provided with two primary windings 4 and 5.

As ilustrated in Fig. 4, the primary windings 4 and 5 are located on separate cores 6 and 7. The core 6 is rectan ular constant electron and is so constructed as to provide a highly saturated magnetic circuit for its primar winding 4 and secondary winding 8 wit normal voltage on the apparatus. The'arrangement of the core and windings illustrated, provides for an appreciable. magnetic leakafge between the windings. The section 5 o the primary winding is wound on an open magnetic core 7 with an auxiliary secondary winding 9. The core 7 is so constructed as to operate far below saturation. The change of voltage at the terminals of the auxiliary secondary winding 9 takes place at a fairly low rate as the primary voltage changes. The core 7 has been shown as an open magnetic core to illustrate this feature. The two primary transformer windings 4 and 5' are connected in series-with each other and by conductors 10 and 11 to the source of energy represented by the mains 12 and 13. The main secondary winding 8 and the auxiliary .secondary winding 9 are also connected in series, but are so connected that the induced electromotive forces oppose each other. The terminals 14, 15 of these windings are connected in series with an adjustable resistig. 1)to the primary of a transance 16,

former 1 1, the secondary of which is connected by conductors 18, 19, to the terminalsv of the cathode 2 of the X-ray tube. In some cases the transformer 17 may beomitted.

The sum of the magnetic fluxes in the saturated and unsaturated magnetic circuit varies in proportion to the voltage variation of the supply circuit 12, 13, but the fluxes in the two secondary windings vary at dif-' erent rates. By properly proportioning the windin secondary windmgs, which are connected in opposition, the sum of the voltage in the conductors14, 15 may be made to decrease t the currents in the primary windings are measured along the horizontal line 23. Since the core 6 ishighly saturated at normal voltages the total electromotive force induced in the main secondary winding 8 varies with the variations of primary current in the general manner re resented by the curve 24, 25.. A change 0 the electro motive force in the auxiliary secondary winding 9 is indicated by the curve 26. This curve 26 is drawn below the horizontal zero line to indicate that this 'electromotive force opposes the electromotive force of the curve 24, 25 the main and auxiliary secondaries 8, 9 being connected in opposition. The resultant secondary voltages across the terminals 14 and 15 therefore may be represented by the curve 27 28. This resultant curve rises rapidly at first over the portion 27, and then bends downwardly. As the current in the primary winding increases with an increase of im ressed electromotive force, the voltage in the conductors 14', 15 decreases.

The cathode 2 and anode 20 of the X-ray tube are connected by conductors 63, 64 to a high potential transformer 65, the primary of which is connected by conductors 66, 67, to the mains 12, 13. In series with the primary of the transformer 65 is a time switch 68, which has been diagrammatically shown in the drawings, and may be of any referred construction. \Vhen the time switch is set to give an exposure of given length, should the voltage in the main conductors 12, 13 vary, for example, should it increase, thereby increasing the voltage across the terminals of the X-ray tube, and consequently increasing the penetrability of the X-rays, then by the action of the described construc- .so as to give over'a workin -stant1all constant radiograp 'c e ect. In-

tion in the filament lightin transformer,

the temperature of the catho e decreases at supply source will result in an increase of voltage of the filament lighting current, in-

creasing the temperature of the cathode and thereby increasin the milliamperage of the current through t e tube and thus compensating for the decrease of impressedvoltag) ran e asu stead o varying the current through the tube the other member of the current-time factor ma be varied, while the current is malntalne constant.

In accordance witha modification of my.

invention illustrated in Fig. 3, the X-ray tube cathode is heated with current of sub-' stantially constant voltage giving a constant cathode temperature giving a substantially constant current-carrying ca acityat operating voltages sufiiciently hig to yield saturation currents and' thelength of time of operation of the tube is varied inversely in proportion to the square of. the voltage in order to givea substantially constant radiographic effect. The current for heating the cathode may be obtained from a separate source of constant voltage, as for exam lo, a

battery, or if desired, the filament lig ting apparatus described in connection with Fig. 1 ma be modified by roperly proportioning t e secondary win ings 8 and 9 to ive a substantially constantvoltage in the a- -ment lighting circuit over a working range.

The X-ray tube and connections have not been illustrated in Fig. 3 as they would appear diagrammatically to be the same as in ig. 1, but the secondaries 8 and 9 are so proportioned that the resultant of the electromotive forces of the coils 8 and 9 will produce current of substantially constant voltage over the operating range. In other words, referring to Fig. 2, the part 28 ofthe resultant current 27 willbe substantially horizontal. In place of the time switch 68, I employ a switch, as illustrated in considerable detail in Fig. 3, which gives a variable time interval, as will nowbe more fully described.

Referring to Fi 3, it will be observed that the time switc has a motor element of the induction. meter type comprising a rotating circular disc 30 supported on a vertical shaft 31 and acted upon by electromagnets 32, 32'. The core of the magnet 32 above the disc 30 is horseshoe shaped and mounted upon its legs are electromagnetic coils 33, 34, which are connected in series with each other and by conductors 35, 36 across the supply conductors 12, 13. The core of the magnet 32' below the disc 30 is E-shaped. Mounted upon its central leg is a coil 37 connected by the conductors 38, 39 across the supply mains 12, 13 in parallel with the series coils 33, 34, thereby obtaining a motor efi'ect in the well known way. The

permanent magnets 40, 41, exercise a mag netic braking or damping effect upon the motor disc 30, so that with avariation of voltage the speed of rotation will vary directly with the square of thevoltage changes.

A movable plate 43 pivoted upon a support 42 carrying the contact making eletors 48, 49 may be connected-in series with the primary of the transformer 23 as indicate in Fig. 3. 1

Whenthe hand switch '50 is closed the electromagnet 45 is energized causing gear train 51 to mesh with the spur gear 44 and producing a clockwise revolution of the ear wheel 52. Mounted upon this gear whee 52 is a pin 53 which engages with a contact 54 when the gear wheel 52 is rotated in a clockwise direction. The contacts 54 and 55 are included in the circuit 48, 49, and are nor-' mally closed. When it is desired to take a radiograph the lever 56 is moved-upon the scale 57 to a desired setting, which has been found by experiment to give a desired exposure for the subject to be radiographed.

This movement of the lever 56 carries a 'zero stop 58 for the pin 53 toward oraway from the movable contact 54 thereby varying the distance thru which the pin is required to travel before opening the contacts 54, 55.

When the switch 50 is closed the X-ray tube begins to function, and as-above described, the ear train is set into motion by the action of the electromagnet 45. By the rotation of the motor element of the switch the pin 53 is carried forward to break the circuit, the rate of motion varying with the square of the voltage thereby varying the exposure time inversely with the square of the voltage so that a substantially constant radiographic effect is produced. In other words, assuming a sub ect requiring an exposure of five seconds with a constant line voltage at the transformer primary of 100 volts, the length of exposure will be automatically decreased to about 4.1 seconds should the line voltage rise to 110 volts.

When the contacts have been opened, the

gear 44 strikes the blank space in the gear 51. When the magnet 45 is deenergized, the ears 44 and 51 are pulled out of mesh by tie s ring 59 and the pin 53 is returned to its ing-gal position against the stop 58 by the spri 60.

The automatic controller or variable time switch shown in Fig. 3 is the invention of Chester I. Hall, and is covered by a patent application, Serial No. 526,994, filed January 4, 1922, by Chester 1. Hall. In a divisional application, Serial No. 634,864 I have made claims on the apparatus and method herein described whereby a constant radiographic effect is obtained by varying the current through the X-ray tube when the applied voltage varies.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An X-ray apparatus adapted for operation from a source of electric energy of variable potential WhlCh consists 1n an X- ray tube operating substantially independently of gaseous ionization, and means responsive to departures of operating voltage from a. predetermined value for varying the time-current factor of said discharge inversely in such measure as to secure a substantially constant radiographic elfect.

2. An X-ray apparatus comprising an X- ray tube, a source of current subject to voltage variations connected to the electrodes of said tube, means for producing at operating voltages a substantially constant currentcarrying capacity in said tube and means whereby the operation of said tube may be set for different time intervals, said means varying the time intervals inversely with the square of the operating voltage, in case said voltage varies, tosecure a predetermined radiographic eifect for any given setting. I

3. An X-ray apparatus adapted for opers ation with current of variable voltage which consists of an X-ray tube, means for generating electrons at the cathode of said tube at a substantially constant rate, means for automatically regulating the length of time of operation of said tube as such inverse function of the supply voltage that the radiographic efl'ect of X-rays generated by said tube for a given setting is substantially constant.

4. An X-ray apparatus adapted for operation from a supply circuit of fluctuating voltage which consists of an X-ray tube having a cathode adapted to be heated, means for supplying said cathode with energy of substantially constant volta e, and a motoroperated'switch for timing intervals during tube, a second transformer having a secondary winding connected to heat said cathode, a common supply circuit forthe rlmary windings of said transformers, sai second transformer being constructed to deliver substantially constant heating current when sup lied with current of variable voltage an switching means constructed to vary the length of operation of said tube to secure a substantially constant radiographic effect. 1

' 6. An X-ray apparatus comprising a transformer, an incandescent cat ode ty e X-ray tube connected to the terminals of t e secondary winding of said transformer,

- means for heating the cathode of said tube to a substantially constant temperature, a switch in circuit with the primary of the transformer, means for setting said switch for different X-ray outputs, and means for varying inversely with'the square of the supply voltage of the transformer the time of operation of said tube to secure a desired radio phic efiect.

7: e combination of an X-ray tube, means for generating electrons at a substantially constant rate at the cathode of said tube, a sapplykeircuit therefor, means for giving sai tu a normal time setting, and means res nsive to variations of voltage in said circuit for varying the length of said setting inversely w1th said voltage varia-- tions to roduce 'a predetermined radiographic e ect.

8. An X-ray apparatus adapted for operation from a' elrcuit of vanabldwoltage, comprising an X-ray tube, circuits for operatively connecting said tube to said source, means for enerating electrons at the cathode of said tube at a substantially constant rate, means for setting the-operation of said tube from said source -for a predetermined output, and means for varying the length of time interval said tube is in operation in such measure as to secure for a given setting a predetermined radiographic efiect regardless of voltage fluctuations of said source. a I 9. The method of operating an X-ra device' by a current of fluctuating vo tage which consists in maintaining through said tube substantially constant whlle varying the time inversely in accordance w1th variations of the square of the applied voltage, thereby obtaining a substantially constant radiographic efiect. 10. The method of operating an X-ray tube of the hot cathode type b an energy supply of fluctuating voltafge w ich consists eatin the cathode 0 said tube with current 0 substantiall constant potential and varying the time interval for a given time setting inversely in accordance with variations of the square of the applied voltage. v

11. In combination, an electric source subject to volta variations, a translating device supplie thereby, means for connecting said device in circuit with said source, a time switch for automatically disconnectin said device after a time interval set at wi said switch comprising means for varying the length of said interval inversel in accordance with the square of thevo tage of thesource in case the voltage varies.

12. In combination an electrical source subject to volt e variations, an incandescent cathode ischarge device sup lied thereby, means for heating said catho e to a substantially constant temperature, means for connecting said device circuit with said source, and a time swltch for auto- -matically disconnectin said device after a set time interval, sai switch comprising means for vary ng said interval lnversely in accordance w1th the square of the voltage of the source when said voltage departs from a predetermined value.

In wltness whereof, I have hereunto set my hand this first day of July 1920.

WILLIAM D. cooLmenf the current 

